Ultra-high temperature ablation behavior of CVD-Hf₅TaC₆ solid solution ceramic coating for C/C composites: Experiment and first-principle calculation

To address the problem that the oxidized layer of HfC coating was loose and porous, Hf_xTa_yC_x+y solid solution with good thermal stability and ablation resistance was proposed as coating for carbon/carbon (C/C) composites. In present work, HfC, TaC and the novel Hf₅TaC₆ solid solution coatings were synthesized on C/C composites by chemical vapor deposition. Combing with the ablation test and density functional theory calculations about oxygen-adsorption energies, the ablation mechanism of HfC, TaC and Hf₅TaC₆ solid solution coatings were investigated. The Hf₅TaC₆ solid solution coating showed superior ablation resistance than that of HfC and TaC coatings, benefitting from the solid-liquid composite oxide layer with HfO₂ and Hf₆Ta₂O₁₇ as solid structure to further stabilize the oxides and resist mechanical erosion, Ta₂O₅ as the liquid filler to heal cracks to inhibit the oxygen infiltration.